1. Field of the Invention
The present invention relates to the update of routing control information. In a network where a plurality of switches each having an ATM (Asynchronous Transfer Mode) interface are interconnected, the switches make SVC (Switched Virtual Circuit) connection with each other by referring to the information produced by exchanging PNNI routing control packets (Hello packets and PTSP (PNNI Topology State Packets)).
2. Description of the Prior Art
PNNI (Private Network to Network Interface) Specification V1. 00 (hereafter called PNNI) from The ATM Forum Technical Committee describes the interface via which the switches in an ATM network make SVC connections. This PNNI contains information on the following:
(a) PNNI routing control packet exchange method and exchange information PA1 (b) Interface requirements for SVC connection and connection establishment procedures PA1 (a) Routing information is generated from the topology information when a call is made from a terminal PA1 (b) Routing information is generated when a PNNI routing control packet is received PA1 (c) Topology information is generated from a received PNNI routing control packet and, at a specified interval, routing information is generated.
The PNNI specifies that topology information be required for generating routing information. The topology information refers to network component information or state information on the network components such as lines and switches. This information is obtained by exchanging PNNI routing control packets the switches within the network.
In the SVC connection mode, each call request from a terminal causes routing information to be read from the destination address field of the call request message to determine the best route (the route composed of lines and switches ensuring the fastest delivery of a message to the destination). One of the following methods is used for generating or updating this routing information:
However, methods (a), (b), and (c) described above have the following problems:
In case of (a), a delay in setting up a call from an originating terminal degrades the overall system performance. In case of (b), there is a possibility that a large number of PNNI routing control packets are received when a line or a switch in the network fails or when a condition (repetitive errors and error recovery processing) occurs. This condition causes routing information to be updated frequently, affecting the system performance. In case of (c), PNNI routing control packet information exchanged in the network is not reflected on the routing information immediately. Therefore, when an SVC connection request is received before routing information is updated by a PNNI routing control packet, the connection request may fail; conversely, when an error is already recovered but the routing information is not yet updated accordingly, the connection request may fail.